SharePoint 2013 MySite quick launch components as below:
- About me(person.aspx) & NewsFeed(default.aspx) are two pages in the
same site collection root site.This site collection will be common
for all users.
- Apps and Blog are 2 seperate sub sites in another Site Collection ie
personal Site Collection of each user.
Clicking on "Apps" will take you to "Site Contents" page of the Personal Site collection root site of particular user.
Clicking on Blog will take you to a blog sub site in the personal site collection of user.
Whenever you deploy custom master page, in order for the master page to applied properly check the following:
- Feature "SharePoint Server Publishing Infrastructure" is
activated for both the site collection (root Site Collection of
MySite and personal site collection of users).
- Make sure "SharePoint Server Publishing" is activated in the
root site of both the site collection as well as the Blog sub site
of the personal site collection of the user.
Make sure "SharePoint Server Publishing" feature is activated in the Blog sub site , since in your case the Apps sub site is displaying the master page changes the "SharePoint Server Publishing Infrastructure" and the "SharePoint Server Publishing" might be already activated.
This Article explains the MySite Quick launch components